Neurological and musculo-skeletal diseases severely impair the complex coordination of finger motion and forces that characterizes our ability to grasp and manipulate objects. Knowledge of the physiological control mechanisms of prehension is essential for an understanding of the pathologies that affect hand function. The long-term objective of the present proposal is to characterize the normal patterns of muscle activation responsible for the control of grasping movements, in particular the strategies used by the nervous system to coordinate the large number of muscles of the hand. This objective will be pursued by studying the simultaneous activation of multiple hand muscles and the coordination of grip forces. The present proposal has three specific aims: to characterize the organization of hand muscle activity as a function of hand and wrist posture (Aim number 1); to determine whether motor unit synchronization is dependent on task constraints (object's size and center of mass location; Aim number 2) and grip type (power vs. precision grip, and object shape; Aim number 3). The proposed studies are based on the hypothesis, supported by previous work, that the coordination of multiple grip forces is based on synergies reducing the number of degrees of freedom that has to be controlled independently. We will determine how the activity of multiple hand muscles is coordinated as a function of finger/wrist posture and task constraints. Hand muscle activity will be measured by intramuscular electromyographic recording as (a) interference multi-unit EMG and (b) single motor unit activity. Contact forces exerted by each finger will be measured in three dimensions by force sensors. The issues examined by this basic research are relevant to efforts in rehabilitation and restoration of hand function.